Itaconate and derivatives reduce interferon responses and inflammation in influenza A virus infection

Itaconate mechanism of action and dissimilation in Mycobacterium tuberculosis

Itaconate, an abundant metabolite produced by macrophages upon interferon-γ stimulation, possesses both antibacterial and immunomodulatory properties. Despite its crucial role in immunity and antimicrobial control, its mechanism of action and dissimilation are poorly understood. Here, we demonstrate that infection of mice with Mycobacterium tuberculosis increases itaconate levels in lung tissues. We also show that exposure to itaconate inhibits M. tuberculosis growth in vitro, in macrophages, and mice. We report that exposure to sodium itaconate (ITA) interferes with the central carbon metabolism of M. tuberculosis. In addition to the inhibition of isocitrate lyase (ICL), we demonstrate that itaconate inhibits aldolase and inosine monophosphate (IMP) dehydrogenase in a concentration-dependent manner. Previous studies have shown that Rv2498c from M. tuberculosis is the bona fide (S)-citramalyl-CoA lyase, but the remaining components of the pathway remain elusive. Here, we report that Rv2503c and Rv3272 possess itaconate:succinyl-CoA transferase activity, and Rv2499c and Rv3389c possess itaconyl-CoA hydratase activity. Relative to the parental and complemented strains, the ΔRv3389c strain of M. tuberculosis was attenuated for growth in itaconate-containing medium, in macrophages, mice, and guinea pigs. The attenuated phenotype of ΔRv3389c strain of M. tuberculosis is associated with a defect in the itaconate dissimilation and propionyl-CoA detoxification pathway. This study thus reveals that multiple metabolic enzymes are targeted by itaconate in M. tuberculosis. Furthermore, we have assigned the two remaining enzymes responsible for the degradation of itaconic acid into pyruvate and acetyl-CoA. Finally, we also demonstrate the importance of enzymes involved in the itaconate dissimilation pathway for M. tuberculosis pathogenesis.

Glutamine-glutamate centered metabolism as the potential therapeutic target against Japanese encephalitis virus-induced encephalitis

BACKGROUND

Japanese encephalitis (JE) induced by Japanese encephalitis virus (JEV) infection is the most prevalent diagnosed epidemic viral encephalitis globally. The underlying pathological mechanisms remain largely unknown. Given that viruses are obligate intracellular parasites, cellular metabolic reprogramming triggered by viral infection is intricately related to the establishment of infection and progression of disease. Therefore, uncovering and manipulating the metabolic reprogramming that underlies viral infection will help elucidate the pathogenic mechanisms and develop novel therapeutic strategies.

METHODS

Metabolomics analysis was performed to comprehensively delineate the metabolic profiles in JEV-infected mice brains and neurons. Metabolic flux analysis, quantitative real-time PCR, western blotting and fluorescence immunohistochemistry were utilized to describe detailed glutamine-glutamate metabolic profiles during JEV infection. Exogenous addition of metabolites and associated compounds and RNA interference were employed to manipulate glutamine-glutamate metabolism to clarify its effects on viral replication. The survival rate, severity of neuroinflammation, and levels of viral replication were assessed to determine the efficacy of glutamine supplementation in JEV-challenged mice.

RESULTS

Here, we have delineated a novel perspective on the pathogenesis of JE by identifying an aberrant low flux in glutamine-glutamate metabolism both in vivo and in vitro, which was critical in the establishment of JEV infection and progression of JE. The perturbed glutamine-glutamate metabolism induced neurotransmitter imbalance and created an immune-inhibitory state with increased gamma-aminobutyric acid/glutamate ratio, thus facilitating efficient viral replication both in JEV-infected neurons and the brain of JEV-infected mice. In addition, viral infection restrained the utilization of glutamine via the glutamate-α-ketoglutaric acid axis in neurons, thus avoiding the adverse effects of glutamine oxidation on viral propagation. As the conversion of glutamine to glutamate was inhibited after JEV infection, the metabolism of glutathione (GSH) was simultaneously impaired, exacerbating oxidative stress in JEV-infected neurons and mice brains and promoting the progression of JE. Importantly, the supplementation of glutamine in vivo alleviated the intracranial inflammation and enhanced the survival of JEV-challenged mice.

CONCLUSION

Altogether, our study highlights an aberrant glutamine-glutamate metabolism during JEV infection and unveils how this facilitates viral replication and promotes JE progression. Manipulation of these metabolic alterations may potentially be exploited to develop therapeutic approaches for JEV infection.

Intrinsic Factors Behind the Long-COVID: V. Immunometabolic Disorders

The complex link between COVID-19 and immunometabolic diseases demonstrates the important interaction between metabolic dysfunction and immunological response during viral infections. Severe COVID-19, defined by a hyperinflammatory state, is greatly impacted by underlying chronic illnesses aggravating the cytokine storm caused by increased levels of Pro-inflammatory cytokines. Metabolic reprogramming, including increased glycolysis and altered mitochondrial function, promotes viral replication and stimulates inflammatory cytokine production, contributing to illness severity. Mitochondrial metabolism abnormalities, strongly linked to various systemic illnesses, worsen metabolic dysfunction during and after the pandemic, increasing cardiovascular consequences. Long COVID-19, defined by chronic inflammation and immune dysregulation, poses continuous problems, highlighting the need for comprehensive therapy solutions that address both immunological and metabolic aspects. Understanding these relationships shows promise for effectively managing COVID-19 and its long-term repercussions, which is the focus of this review paper.

Itaconate facilitates viral infection via alkylating GDI2 and retaining Rab GTPase on the membrane

Metabolic reprogramming of host cells plays critical roles during viral infection. Itaconate, a metabolite produced from cis-aconitate in the tricarboxylic acid cycle (TCA) by immune responsive gene 1 (IRG1), is involved in regulating innate immune response and pathogen infection. However, its involvement in viral infection and underlying mechanisms remain incompletely understood. Here, we demonstrate that the IRG1-itaconate axis facilitates the infections of VSV and IAV in macrophages and epithelial cells via Rab GTPases redistribution. Mechanistically, itaconate promotes the retention of Rab GTPases on the membrane via directly alkylating Rab GDP dissociation inhibitor beta (GDI2), the latter of which extracts Rab GTPases from the membrane to the cytoplasm. Multiple alkylated residues by itaconate, including cysteines 203, 335, and 414 on GDI2, were found to be important during viral infection. Additionally, this effect of itaconate needs an adequate distribution of Rab GTPases on the membrane, which relies on Rab geranylgeranyl transferase (GGTase-II)-mediated geranylgeranylation of Rab GTPases. The single-cell RNA sequencing data revealed high expression of IRG1 primarily in neutrophils during viral infection. Co-cultured and in vivo animal experiments demonstrated that itaconate produced by neutrophils plays a dominant role in promoting viral infection. Overall, our study reveals that neutrophils-derived itaconate facilitates viral infection via redistribution of Rab GTPases, suggesting potential targets for antiviral therapy.

Reprogramming macrophage metabolism following myocardial infarction: A neglected piece of a therapeutic opportunity

Given the global prevalence of myocardial infarction (MI) as the leading cause of mortality, there is an urgent need to devise novel strategies that target reducing infarct size, accelerating cardiac tissue repair, and preventing detrimental left ventricular (LV) remodeling. Macrophages, as a predominant type of innate immune cells, undergo metabolic reprogramming following MI, resulting in alterations in function and phenotype that significantly impact the progression of MI size and LV remodeling. This article aimed to delineate the characteristics of macrophage metabolites during reprogramming in MI and elucidate their targets and functions in cardioprotection. Furthermore, we summarize the currently proposed regulatory mechanisms of macrophage metabolic reprogramming and identify the regulators derived from endogenous products and natural small molecules. Finally, we discussed the challenges of macrophage metabolic reprogramming in the treatment of MI, with the goal of inspiring further fundamental and clinical research into reprogramming macrophage metabolism and validating its potential therapeutic targets for MI.

Fructose-1,6-diphosphate inhibits viral replication by promoting the lysosomal degradation of HMGB1 and blocking the binding of HMGB1 to the viral genome

Fructose-1,6-diphosphate (FBP), a key glycolytic metabolite, is recognized for its cytoprotective effects during stress. However, the role of FBP in viral infections is unknown. Here, we demonstrate that virus-infected cells exhibit elevated FBP levels. Exogenous FBP inhibits both RNA and DNA virus infections in vitro and in vivo. Modulating intracellular FBP levels by regulating the expression of the metabolic enzymes FBP1 and PFK1 significantly impacts viral infections. Mechanistically, the inhibitory effects of FBP are not a result of altered viral adhesion or entry and are largely independent of type I interferon-mediated immune responses; rather, they occur through modulation of HMGB1. During viral infections, FBP predominantly reduces the protein levels of HMGB1 by facilitating its lysosomal degradation. Furthermore, FBP interacts with HMGB1 and disrupts the binding of HMGB1 to viral genomes, thereby further inhibiting viral replication. Our findings underscore the potential of FBP as a therapeutic target for controlling viral infections.

Immunometabolism: signaling pathways, homeostasis, and therapeutic targets

Immunometabolism plays a central role in sustaining immune system functionality and preserving physiological homeostasis within the organism. During the differentiation and activation, immune cells undergo metabolic reprogramming mediated by complex signaling pathways. Immune cells maintain homeostasis and are influenced by metabolic microenvironmental cues. A series of immunometabolic enzymes modulate immune cell function by metabolizing nutrients and accumulating metabolic products. These enzymes reverse immune cells' differentiation, disrupt intracellular signaling pathways, and regulate immune responses, thereby influencing disease progression. The huge population of immune metabolic enzymes, the ubiquity, and the complexity of metabolic regulation have kept the immune metabolic mechanisms related to many diseases from being discovered, and what has been revealed so far is only the tip of the iceberg. This review comprehensively summarized the immune metabolic enzymes' role in multiple immune cells such as T cells, macrophages, natural killer cells, and dendritic cells. By classifying and dissecting the immunometabolism mechanisms and the implications in diseases, summarizing and analyzing advancements in research and clinical applications of the inhibitors targeting these enzymes, this review is intended to provide a new perspective concerning immune metabolic enzymes for understanding the immune system, and offer novel insight into future therapeutic interventions.

Differential transcriptomic host responses in the early phase of viral and bacterial infections in human lung tissue explants ex vivo

BACKGROUND

The first 24 h of infection represent a critical time window in interactions between pathogens and host tissue. However, it is not possible to study such early events in human lung during natural infection due to lack of clinical access to tissue this early in infection. We, therefore, applied RNA sequencing to ex vivo cultured human lung tissue explants (HLTE) from patients with emphysema to study global changes in small noncoding RNA, mRNA, and long noncoding RNA (lncRNA, lincRNA) populations during the first 24 h of infection with influenza A virus (IAV), Mycobacterium bovis Bacille Calmette-Guerin (BCG), and Pseudomonas aeruginosa.

RESULTS

Pseudomonas aeruginosa caused the strongest expression changes and was the only pathogen that notably affected expression of microRNA and PIWI-associated RNA. The major classes of long RNAs (> 100 nt) were represented similarly among the RNAs that were differentially expressed upon infection with the three pathogens (mRNA 77-82%; lncRNA 15-17%; pseudogenes 4-5%), but lnc-DDX60-1, RP11-202G18.1, and lnc-THOC3-2 were part of an RNA signature (additionally containing SNX10 and SLC8A1) specifically associated with IAV infection. IAV infection induced brisk interferon responses, CCL8 being the most strongly upregulated mRNA. Single-cell RNA sequencing identified airway epithelial cells and macrophages as the predominant IAV host cells, but inflammatory responses were also detected in cell types expressing few or no IAV transcripts. Combined analysis of bulk and single-cell RNAseq data identified a set of 6 mRNAs (IFI6, IFI44L, IRF7, ISG15, MX1, MX2) as the core transcriptomic response to IAV infection. The two bacterial pathogens induced qualitatively very similar changes in mRNA expression and predicted signaling pathways, but the magnitude of change was greater in P. aeruginosa infection. Upregulation of GJB2, VNN1, DUSP4, SerpinB7, and IL10, and downregulation of PKMYT1, S100A4, GGTA1P, and SLC22A31 were most strongly associated with bacterial infection.

CONCLUSIONS

Human lung tissue mounted substantially different transcriptomic responses to infection by IAV than by BCG and P. aeruginosa, whereas responses to these two divergent bacterial pathogens were surprisingly similar. This HLTE model should prove useful for RNA-directed pathogenesis research and tissue biomarker discovery during the early phase of infections, both at the tissue and single-cell level.

Multifaceted metabolic role of infections in the tumor microenvironment

The impact of bacteria and viruses on tumor growth has long been recognized. In recent decades, interest in the role of microorganisms in the tumor microenvironment (TME) has expanded. Infections induce metabolic reprogramming and influence immune responses within the TME that may either support proliferation and metastasis or limit tumor growth. The natural ability to infect cells and alter the TME is also utilized for cancer detection and treatment. In this review, we discuss recent discoveries about the mechanisms of bacteria and viruses affecting TME, as well as strategies in cancer therapy focusing on metabolic alterations. Infections with engineered bacteria and viruses represent promising therapeutic approaches to develop novel and more effective therapies to constrain tumor growth.

The role and therapeutic potential of itaconate in lung disease

Lung diseases triggered by endogenous or exogenous factors have become a major concern, with high morbidity and mortality rates, especially after the coronavirus disease 2019 (COVID-19) pandemic. Inflammation and an over-activated immune system can lead to a cytokine cascade, resulting in lung dysfunction and injury. Itaconate, a metabolite produced by macrophages, has been reported as an effective anti-inflammatory and anti-oxidative stress agent with significant potential in regulating immunometabolism. As a naturally occurring metabolite in immune cells, itaconate has been identified as a potential therapeutic target in lung diseases through its role in regulating inflammation and immunometabolism. This review focuses on the origin, regulation, and function of itaconate in lung diseases, and briefly discusses its therapeutic potential.

The potential therapeutic role of itaconate and mesaconate on the detrimental effects of LPS-induced neuroinflammation in the brain

Despite advances in antimicrobial and anti-inflammatory treatment, inflammation and its consequences remain a major challenge in the field of medicine. Inflammatory reactions can lead to life-threatening conditions such as septic shock, while chronic inflammation has the potential to worsen the condition of body tissues and ultimately lead to significant impairment of their functionality. Although the central nervous system has long been considered immune privileged to peripheral immune responses, recent research has shown that strong immune responses in the periphery also affect the brain, leading to reactive microglia, which belong to the innate immune system and reside in the brain, and neuroinflammation. The inflammatory response is primarily a protective mechanism to defend against pathogens and tissue damage. However, excessive and chronic inflammation can have negative effects on neuronal structure and function. Neuroinflammation underlies the pathogenesis of many neurological and neurodegenerative diseases and can accelerate their progression. Consequently, targeting inflammatory signaling pathways offers potential therapeutic strategies for various neuropathological conditions, particularly Parkinson's and Alzheimer's disease, by curbing inflammation. Here the blood-brain barrier is a major hurdle for potential therapeutic strategies, therefore it would be highly advantageous to foster and utilize brain innate anti-inflammatory mechanisms. The tricarboxylic acid cycle-derived metabolite itaconate is highly upregulated in activated macrophages and has been shown to act as an immunomodulator with anti-inflammatory and antimicrobial functions. Mesaconate, an isomer of itaconate, similarly reduces the inflammatory response in macrophages. Nevertheless, most studies have focused on its esterified forms and its peripheral effects, while its influence on the CNS remained largely unexplored. Therefore, this study investigated the immunomodulatory and therapeutic potential of endogenously synthesized itaconate and its isomer mesaconate in lipopolysaccharide (LPS)-induced neuroinflammatory processes. Our results show that both itaconate and mesaconate reduce LPS-induced neuroinflammation, as evidenced by lower levels of inflammatory mediators, reduced microglial reactivity and a rescue of synaptic plasticity, the cellular correlate of learning and memory processes in the brain. Overall, this study emphasizes that both itaconate and mesaconate have therapeutic potential for neuroinflammatory processes in the brain and are of remarkable importance due to their endogenous origin and production, which usually leads to high tolerance.

Suppression of HIV-TAT and cocaine-induced neurotoxicity and inflammation by cell penetrable itaconate esters

HIV-associated neurological disorder (HAND) is a serious complication of HIV infection marked by neurotoxicity induced by viral proteins like Tat. Substance abuse exacerbates neurocognitive impairment in people living with HIV. There is an urgent need for therapeutic strategies to combat HAND comorbid with Cocaine Use Disorder (CUD). Our analysis of HIV and cocaine-induced transcriptomes in primary cortical cultures revealed significant overexpression of the macrophage-specific gene aconitate decarboxylase 1 (Acod1). The ACOD1 protein converts the tricarboxylic acid intermediate cis-aconitate into itaconate during the activation of inflammation. Itaconate then facilitates cytokine production and activates anti-inflammatory transcription factors, shielding macrophages from infection-induced cell death. However, the immunometabolic function of itaconate was unexplored in HIV and cocaine-exposed microglia. We assessed the potential of 4-octyl-itaconate (4OI), a cell-penetrable ester form of itaconate known for its anti-inflammatory properties. When primary cortical cultures exposed to Tat and cocaine were treated with 4OI, microglial cell number increased and the morphological altercations induced by Tat and cocaine were reversed. Microglial cells also appeared more ramified, resembling the quiescent microglia. 4OI treatment inhibited secretion of the proinflammatory cytokines IL-1α, IL-1β, IL-6, and MIP1-α induced by Tat and cocaine. Transcriptome profiling determined that Nrf2 target genes were significantly activated in Tat and 4OI treated cultures relative to Tat alone. Further, genes associated with cytoskeleton dynamics in inflammatory microglia were downregulated by 4OI treatment. Together, the results strongly suggest 4-octyl-itaconate holds promise as a potential candidate for therapeutic development to treat HAND coupled with CUD comorbidities.

Itaconate protects ferroptotic neurons by alkylating GPx4 post stroke

Neuronal ferroptosis plays a key role in neurologic deficits post intracerebral hemorrhage (ICH). However, the endogenous regulation of rescuing ferroptotic neurons is largely unexplored. Here, we analyzed the integrated alteration of metabolomic landscape after ICH using LC-MS and MALDI-TOF/TOF MS, and demonstrated that aconitate decarboxylase 1 (Irg1) and its product itaconate, a derivative of the tricarboxylic acid cycle, were protectively upregulated. Deficiency of Irg1 or depletion of neuronal Irg1 in striatal neurons was shown to exaggerate neuronal loss and behavioral dysfunction in an ICH mouse model using transgenic mice. Administration of 4-Octyl itaconate (4-OI), a cell-permeable itaconate derivative, and neuronal Irg1 overexpression protected neurons in vivo. In addition, itaconate inhibited ferroptosis in cortical neurons derived from mouse and human induced pluripotent stem cells in vitro. Mechanistically, we demonstrated that itaconate alkylated glutathione peroxidase 4 (GPx4) on its cysteine 66 and the modification allosterically enhanced GPx4's enzymatic activity by using a bioorthogonal probe, itaconate-alkyne (ITalk), and a GPx4 activity assay using phosphatidylcholine hydroperoxide. Altogether, our research suggested that Irg1/itaconate-GPx4 axis may be a future therapeutic strategy for protecting neurons from ferroptosis post ICH.

Immunometabolites in viral infections: Action mechanism and function

The interplay between viral pathogens and host metabolism plays a pivotal role in determining the outcome of viral infections. Upon viral detection, the metabolic landscape of the host cell undergoes significant changes, shifting from oxidative respiration via the tricarboxylic acid (TCA) cycle to increased aerobic glycolysis. This metabolic shift is accompanied by elevated nutrient accessibility, which is vital for cell function, development, and proliferation. Furthermore, depositing metabolites derived from fatty acids, TCA intermediates, and amino acid catabolism accelerates the immunometabolic transition, facilitating pro-inflammatory and antimicrobial responses. Immunometabolites refer to small molecules involved in cellular metabolism regulating the immune response. These molecules include nutrients, such as glucose and amino acids, along with metabolic intermediates and signaling molecules adenosine, lactate, itaconate, succinate, kynurenine, and prostaglandins. Emerging evidence suggests that immunometabolites released by immune cells establish a complex interaction network within local niches, orchestrating and fine-tuning immune responses during viral diseases. However, our current understanding of the immense capacity of metabolites to convey essential cell signals from one cell to another or within cellular compartments remains incomplete. Unraveling these complexities would be crucial for harnessing the potential of immunometabolites in therapeutic interventions. In this review, we discuss specific immunometabolites and their mechanisms of action in viral infections, emphasizing recent findings and future directions in this rapidly evolving field.

The Role of the Nrf2 Pathway in Airway Tissue Damage Due to Viral Respiratory Infections

Respiratory viruses constitute a significant cause of illness and death worldwide. Respiratory virus-associated injuries include oxidative stress, ferroptosis, inflammation, pyroptosis, apoptosis, fibrosis, autoimmunity, and vascular injury. Several studies have demonstrated the involvement of the nuclear factor erythroid 2-related factor 2 (Nrf2) in the pathophysiology of viral infection and associated complications. It has thus emerged as a pivotal player in cellular defense mechanisms against such damage. Here, we discuss the impact of Nrf2 activation on airway injuries induced by respiratory viruses, including viruses, coronaviruses, rhinoviruses, and respiratory syncytial viruses. The inhibition or deregulation of Nrf2 pathway activation induces airway tissue damage in the presence of viral respiratory infections. In contrast, Nrf2 pathway activation demonstrates protection against tissue and organ injuries. Clinical trials involving Nrf2 agonists are needed to define the effect of Nrf2 therapeutics on airway tissues and organs damaged by viral respiratory infections.

NRF2-mediated regulation of lipid pathways in viral infection

The first line of defense against viral infection of the host cell is the cellular lipid membrane, which is also a crucial first site of contact for viruses. Lipids may sometimes be used as viral receptors by viruses. For effective infection, viruses significantly depend on lipid rafts during the majority of the viral life cycle. It has been discovered that different viruses employ different lipid raft modification methods for attachment, internalization, membrane fusion, genome replication, assembly, and release. To preserve cellular homeostasis, cells have potent antioxidant, detoxifying, and cytoprotective capabilities. Nuclear factor erythroid 2-related factor 2 (NRF2), widely expressed in many tissues and cell types, is one crucial component controlling electrophilic and oxidative stress (OS). NRF2 has recently been given novel tasks, including controlling inflammation and antiviral interferon (IFN) responses. The activation of NRF2 has two effects: it may both promote and prevent the development of viral diseases. NRF2 may also alter the host's metabolism and innate immunity during viral infection. However, its primary function in viral infections is to regulate reactive oxygen species (ROS). In several research, the impact of NRF2 on lipid metabolism has been examined. NRF2 is also involved in the control of lipids during viral infection. We evaluated NRF2's function in controlling viral and lipid infections in this research. We also looked at how lipids function in viral infections. Finally, we investigated the role of NRF2 in lipid modulation during viral infections.

Octyl itaconate enhances VSVΔ51 oncolytic virotherapy by multitarget inhibition of antiviral and inflammatory pathways

The presence of heterogeneity in responses to oncolytic virotherapy poses a barrier to clinical effectiveness, as resistance to this treatment can occur through the inhibition of viral spread within the tumor, potentially leading to treatment failures. Here we show that 4-octyl itaconate (4-OI), a chemical derivative of the Krebs cycle-derived metabolite itaconate, enhances oncolytic virotherapy with VSVΔ51 in various models including human and murine resistant cancer cell lines, three-dimensional (3D) patient-derived colon tumoroids and organotypic brain tumor slices. Furthermore, 4-OI in combination with VSVΔ51 improves therapeutic outcomes in a resistant murine colon tumor model. Mechanistically, we find that 4-OI suppresses antiviral immunity in cancer cells through the modification of cysteine residues in MAVS and IKKβ independently of the NRF2/KEAP1 axis. We propose that the combination of a metabolite-derived drug with an oncolytic virus agent can greatly improve anticancer therapeutic outcomes by direct interference with the type I IFN and NF-κB-mediated antiviral responses.

Metabolic regulation of type I interferon production

Over the past decade, there has been a surge in discoveries of how metabolic pathways regulate immune cell function in health and disease, establishing the field of immunometabolism. Specifically, pathways such as glycolysis, the tricarboxylic acid (TCA) cycle, and those involving lipid metabolism have been implicated in regulating immune cell function. Viral infections cause immunometabolic changes which lead to antiviral immunity, but little is known about how metabolic changes regulate interferon responses. Interferons are critical cytokines in host defense, rapidly induced upon pathogen recognition, but are also involved in autoimmune diseases. This review summarizes how metabolic change impacts interferon production. We describe how glycolysis, lipid metabolism (specifically involving eicosanoids and cholesterol), and the TCA cycle-linked intermediates itaconate and fumarate impact type I interferons. Targeting these metabolic changes presents new therapeutic possibilities to modulate type I interferons during host defense or autoimmune disorders.

Evolution of innate immunity: lessons from mammalian models shaping our current view of insect immunity

The innate immune system, a cornerstone for organismal resilience against environmental and microbial insults, is highly conserved across the evolutionary spectrum, underpinning its pivotal role in maintaining homeostasis and ensuring survival. This review explores the evolutionary parallels between mammalian and insect innate immune systems, illuminating how investigations into these disparate immune landscapes have been reciprocally enlightening. We further delve into how advancements in mammalian immunology have enriched our understanding of insect immune responses, highlighting the intertwined evolutionary narratives and the shared molecular lexicon of immunity across these organisms. Therefore, this review posits a holistic understanding of innate immune mechanisms, including immunometabolism, autophagy and cell death. The examination of how emerging insights into mammalian and vertebrate immunity inform our understanding of insect immune responses and their implications for vector-borne disease transmission showcases the imperative for a nuanced comprehension of innate immunity's evolutionary tale. This understanding is quintessential for harnessing innate immune mechanisms' potential in devising innovative disease mitigation strategies and promoting organismal health across the animal kingdom.

Integrating single-cell RNA sequencing data to genome-wide association analysis data identifies significant cell types in influenza A virus infection and COVID-19

With the global pandemic of COVID-19, the research on influenza virus has entered a new stage, but it is difficult to elucidate the pathogenesis of influenza disease. Genome-wide association studies (GWASs) have greatly shed light on the role of host genetic background in influenza pathogenesis and prognosis, whereas single-cell RNA sequencing (scRNA-seq) has enabled unprecedented resolution of cellular diversity and in vivo following influenza disease. Here, we performed a comprehensive analysis of influenza GWAS and scRNA-seq data to reveal cell types associated with influenza disease and provide clues to understanding pathogenesis. We downloaded two GWAS summary data, two scRNA-seq data on influenza disease. After defining cell types for each scRNA-seq data, we used RolyPoly and LDSC-cts to integrate GWAS and scRNA-seq. Furthermore, we analyzed scRNA-seq data from the peripheral blood mononuclear cells (PBMCs) of a healthy population to validate and compare our results. After processing the scRNA-seq data, we obtained approximately 70 000 cells and identified up to 13 cell types. For the European population analysis, we determined an association between neutrophils and influenza disease. For the East Asian population analysis, we identified an association between monocytes and influenza disease. In addition, we also identified monocytes as a significantly related cell type in a dataset of healthy human PBMCs. In this comprehensive analysis, we identified neutrophils and monocytes as influenza disease-associated cell types. More attention and validation should be given in future studies.

Itaconate as a key regulator of respiratory disease

Macrophage activation results in the accumulation of endogenous metabolites capable of adopting immunomodulatory roles; one such bioactive metabolite is itaconate. After macrophage stimulation, the TCA-cycle intermediate cis-aconitate is converted to itaconate (by aconitate decarboxylase-1, ACOD1) in the mitochondrial matrix. Recent studies have highlighted the potential of targeting itaconate as a therapeutic strategy for lung diseases such as asthma, idiopathic pulmonary fibrosis (IPF), and respiratory infections. This review aims to bring together evidence which highlights a role for itaconate in chronic lung diseases (such as asthma and pulmonary fibrosis) and respiratory infections (such as SARS-CoV-2, influenza and Mycobacterium tuberculosis infection). A better understanding of the role of itaconate in lung disease could pave the way for novel therapeutic interventions and improve patient outcomes in respiratory disorders.

Anti-Necroptotic Effects of Itaconate and its Derivatives

Itaconate is an unsaturated dicarboxylic acid that is derived from the decarboxylation of the Krebs cycle intermediate cis-aconitate and has been shown to exhibit anti-inflammatory and anti-bacterial/viral properties. But the mechanisms underlying itaconate's anti-inflammatory activities are not fully understood. Necroptosis, a lytic form of regulated cell death (RCD), is mediated by receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL) signaling. It has been involved in the pathogenesis of organ injury in many inflammatory diseases. In this study, we aimed to explore whether itaconate and its derivatives can inhibit necroptosis in murine macrophages, a mouse MPC-5 cell line and a human HT-29 cell line in response to different necroptotic activators. Our results showed that itaconate and its derivatives dose-dependently inhibited necroptosis, among which dimethyl itaconate (DMI) was the most effective one. Mechanistically, itaconate and its derivatives inhibited necroptosis by suppressing the RIPK1/RIPK3/MLKL signaling and the oligomerization of MLKL. Furthermore, DMI promoted the nuclear translocation of Nrf2 that is a critical regulator of intracellular redox homeostasis, and reduced the levels of intracellular reactive oxygen species (ROS) and mitochondrial superoxide (mtROS) that were induced by necroptotic activators. Consistently, DMI prevented the loss of mitochondrial membrane potential induced by the necroptotic activators. In addition, DMI mitigated caerulein-induced acute pancreatitis in mice accompanied by reduced activation of the necroptotic signaling in vivo. Collectively, our study demonstrates that itaconate and its derivatives can inhibit necroptosis by suppressing the RIPK1/RIPK3/MLKL signaling, highlighting their potential applications for treating necroptosis-associated diseases.

Time-Course Transcriptome Analysis Reveals Distinct Phases and Identifies Two Key Genes during Severe Fever with Thrombocytopenia Syndrome Virus Infection in PMA-Induced THP-1 Cells

In recent years, there have been significant advancements in the research of Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV). However, several limitations and challenges still exist. For instance, researchers face constraints regarding experimental conditions and the feasibility of sample acquisition for studying SFTSV. To enhance the quality and comprehensiveness of SFTSV research, we opted to employ PMA-induced THP-1 cells as a model for SFTSV infection. Multiple time points of SFTSV infection were designed to capture the dynamic nature of the virus-host interaction. Through a comprehensive analysis utilizing various bioinformatics approaches, including diverse clustering methods, MUfzz analysis, and LASSO/Cox machine learning, we performed dynamic analysis and identified key genes associated with SFTSV infection at the host cell transcriptomic level. Notably, successful clustering was achieved for samples infected at different time points, leading to the identification of two important genes, PHGDH and NLRP12. And these findings may provide valuable insights into the pathogenesis of SFTSV and contribute to our understanding of host-virus interactions.

Itaconate suppresses atherosclerosis by activating a Nrf2-dependent antiinflammatory response in macrophages in mice

Itaconate has emerged as a critical immunoregulatory metabolite. Here, we examined the therapeutic potential of itaconate in atherosclerosis. We found that both itaconate and the enzyme that synthesizes it, aconitate decarboxylase 1 (Acod1, also known as immune-responsive gene 1 [IRG1]), are upregulated during atherogenesis in mice. Deletion of Acod1 in myeloid cells exacerbated inflammation and atherosclerosis in vivo and resulted in an elevated frequency of a specific subset of M1-polarized proinflammatory macrophages in the atherosclerotic aorta. Importantly, Acod1 levels were inversely correlated with clinical occlusion in atherosclerotic human aorta specimens. Treating mice with the itaconate derivative 4-octyl itaconate attenuated inflammation and atherosclerosis induced by high cholesterol. Mechanistically, we found that the antioxidant transcription factor, nuclear factor erythroid 2-related factor 2 (Nrf2), was required for itaconate to suppress macrophage activation induced by oxidized lipids in vitro and to decrease atherosclerotic lesion areas in vivo. Overall, our work shows that itaconate suppresses atherogenesis by inducing Nrf2-dependent inhibition of proinflammatory responses in macrophages. Activation of the itaconate pathway may represent an important approach to treat atherosclerosis.

Metabolite itaconate in host immunoregulation and defense

Metabolic states greatly influence functioning and differentiation of immune cells. Regulating the metabolism of immune cells can effectively modulate the host immune response. Itaconate, an intermediate metabolite derived from the tricarboxylic acid (TCA) cycle of immune cells, is produced through the decarboxylation of cis-aconitate by cis-aconitate decarboxylase in the mitochondria. The gene encoding cis-aconitate decarboxylase is known as immune response gene 1 (IRG1). In response to external proinflammatory stimulation, macrophages exhibit high IRG1 expression. IRG1/itaconate inhibits succinate dehydrogenase activity, thus influencing the metabolic status of macrophages. Therefore, itaconate serves as a link between macrophage metabolism, oxidative stress, and immune response, ultimately regulating macrophage function. Studies have demonstrated that itaconate acts on various signaling pathways, including Keap1-nuclear factor E2-related factor 2-ARE pathways, ATF3-IκBζ axis, and the stimulator of interferon genes (STING) pathway to exert antiinflammatory and antioxidant effects. Furthermore, several studies have reported that itaconate affects cancer occurrence and development through diverse signaling pathways. In this paper, we provide a comprehensive review of the role IRG1/itaconate and its derivatives in the regulation of macrophage metabolism and functions. By furthering our understanding of itaconate, we intend to shed light on its potential for treating inflammatory diseases and offer new insights in this field.

Itaconate inhibits SYK through alkylation and suppresses inflammation against hvKP induced intestinal dysbiosis

Hypervirulent Klebsiella pneumoniae (hvKP) is a highly lethal opportunistic pathogen that elicits more severe inflammatory responses compared to classical Klebsiella pneumoniae (cKP). In this study, we investigated the interaction between hvKP infection and the anti-inflammatory immune response gene 1 (IRG1)-itaconate axis. Firstly, we demonstrated the activation of the IRG1-itaconate axis induced by hvKP, with a dependency on SYK signaling rather than STING. Importantly, we discovered that exogenous supplementation of itaconate effectively inhibited excessive inflammation by directly inhibiting SYK kinase at the 593 site through alkylation. Furthermore, our study revealed that itaconate effectively suppressed the classical activation phenotype (M1 phenotype) and macrophage cell death induced by hvKP. In vivo experiments demonstrated that itaconate administration mitigated hvKP-induced disturbances in intestinal immunopathology and homeostasis, including the restoration of intestinal barrier integrity and alleviation of dysbiosis in the gut microbiota, ultimately preventing fatal injury. Overall, our study expands the current understanding of the IRG1-itaconate axis in hvKP infection, providing a promising foundation for the development of innovative therapeutic strategies utilizing itaconate for the treatment of hvKP infections.

Modeling Human Respiratory Syncytial Virus (RSV) Infection: Recent Contributions and Future Directions Using the Calf Model of Bovine RSV Disease

The human orthopneumovirus (human respiratory syncytial virus [RSV]) is a leading cause of respiratory disease in children worldwide and a significant cause of infant mortality in low- and middle-income countries. The natural immune response to the virus has a preponderant role in disease progression, with a rapid neutrophil infiltration and dysbalanced T cell response in the lungs associated with severe disease in infants. The development of preventive interventions against human RSV has been difficult partly due to the need to use animal models that only partially recapitulate the immune response as well as the disease progression seen in human infants. In this brief review, we discuss the contributions of the calf model of RSV infection to understanding immunity to RSV and in developing vaccine and drug candidates, focusing on recent research areas. We propose that the bovine model of RSV infection is a valuable alternative for assessing the translational potential of interventions aimed at the human population.

Suppression of HIV and cocaine-induced neurotoxicity and inflammation by cell penetrable itaconate esters

HIV-associated neurological disorder (HAND) is a serious complication of HIV infection, marked by neurotoxicity induced by viral proteins like Tat. Substance abuse exacerbates neurocognitive impairment in people living with HIV. There is an urgent need for effective therapeutic strategies to combat HAND comorbid with Cocaine Use Disorder (CUD). Our analysis of the HIV and cocaine-induced transcriptomes in primary cortical cultures revealed a significant overexpression of the macrophage-specific gene, aconitate decarboxylase 1 (Acod1), caused by the combined insults of HIV and cocaine. ACOD1 protein converts the tricarboxylic acid intermediate cis-aconitate into itaconate during the activation of inflammation. The itaconate produced facilitates cytokine production and subsequently activates anti-inflammatory transcription factors, shielding macrophages from infection-induced cell death. While the role of itaconate' in limiting inflammation has been studied in peripheral macrophages, its immunometabolic function remains unexplored in HIV and cocaine-exposed microglia. We assessed in this model system the potential of 4-octyl-itaconate (4OI), a cell-penetrable esterified form of itaconate known for its potent anti-inflammatory properties and potential therapeutic applications. We administered 4OI to primary cortical cultures exposed to Tat and cocaine. 4OI treatment increased the number of microglial cells in both untreated and Tat±Cocaine-treated cultures and also reversed the morphological altercations induced by Tat and cocaine. In the presence of 4OI, microglial cells also appeared more ramified, resembling the quiescent microglia. Consistent with these results, 4OI treatment inhibited the secretion of the proinflammatory cytokines IL-1α, IL-1β, IL-6, and MIP1-α induced by Tat and cocaine. Transcriptome profiling further determined that Nrf2 target genes such as NAD(P)H quinone oxidoreductase 1 (Nqo1), Glutathione S-transferase Pi (Gstp1), and glutamate cysteine ligase catalytic (Gclc), were most significantly activated in Tat-4OI treated cultures, relative to Tat alone. Further, genes associated with cytoskeleton dynamics in inflammatory microglia were downregulated by 4OI treatment. Together, the results strongly suggest 4-octyl-itaconate holds promise as a potential candidate for therapeutic development aimed at addressing HAND coupled with CUD comorbidities.

Sodium taurocholate hydrate inhibits influenza virus replication and suppresses influenza a Virus-triggered inflammation in vitro and in vivo

Influenza A virus is an important respiratory pathogen that poses serious threats to human health. Owing to the high mutation rate of viral genes, weaker cross-protection of vaccines, and rapid emergence of drug resistance, there is an urgent need to develop new antiviral drugs against influenza viruses. Taurocholic acid is a primary bile acid that promotes digestion, absorption, and excretion of dietary lipids. Here, we demonstrate that sodium taurocholate hydrate (STH) exhibits broad-spectrum antiviral activity against influenza strains H5N6, H1N1, H3N2, H5N1, and H9N2 in vitro. STH significantly inhibited the early stages of influenza A virus replication. The levels of influenza virus viral RNA (vRNA), complementary RNA (cRNA), and mRNA were specifically reduced in virus-infected cells following STH treatment. In vivo, STH treatment of infected mice alleviated clinical signs and reduced weight loss and mortality. STH also reduced TNF-α, IL-1β, and IL-6 overexpression. STH significantly inhibited the upregulation of TLR4 and the NF-kB family member p65, both in vivo and in vitro. These results suggest that STH exerts a protective effect against influenza infection via suppression of the NF-kB pathway, highlighting the potential use of STH as a drug for treating influenza infection.

Controlling viral inflammatory lesions by rebalancing immune response patterns

In this review, we discuss a variety of immune modulating approaches that could be used to counteract tissue-damaging viral immunoinflammatory lesions which typify many chronic viral infections. We make the point that in several viral infections the lesions can be largely the result of one or more aspects of the host response mediating the cell and tissue damage rather than the virus itself being directly responsible. However, within the reactive inflammatory lesions along with the pro-inflammatory participants there are also other aspects of the host response that may be acting to constrain the activity of the damaging components and are contributing to resolution. This scenario should provide the prospect of rebalancing the contributions of different host responses and hence diminish or even fully control the virus-induced lesions. We identify several aspects of the host reactions that influence the pattern of immune responsiveness and describe approaches that have been used successfully, mainly in model systems, to modulate the activity of damaging participants and which has led to lesion control. We emphasize examples where such therapies are, or could be, translated for practical use in the clinic to control inflammatory lesions caused by viral infections.

The Dual Role of ACOD1 in Inflammation

Immunometabolism is an interdisciplinary field that focuses on the relationship between metabolic pathways and immune responses. Dysregulated immunometabolism contributes to many pathological settings, such as cytokine storm or immune tolerance. Aconitate decarboxylase 1 (ACOD1, also known as immunoresponsive gene 1), the mitochondrial enzyme responsible for catalyzing itaconate production, was originally identified as a bacterial LPS-inducible gene involved in innate immunity in mouse macrophages. We now know that the upregulation of ACOD1 expression in immune or nonimmune cells plays a context-dependent role in metabolic reprogramming, signal transduction, inflammasome regulation, and protein modification. The emerging function of ACOD1 in inflammation and infection is a double-edged sword. In this review, we discuss how ACOD1 regulates anti-inflammatory or proinflammatory responses in an itaconate-dependent or -independent manner. Further understanding of ACOD1 expression and function may pave the way for the development of precision therapies for inflammatory diseases.

NRF2 activators inhibit influenza A virus replication by interfering with nucleo-cytoplasmic export of viral RNPs in an NRF2-independent manner

In addition to antioxidative and anti-inflammatory properties, activators of the cytoprotective nuclear factor erythroid-2-like-2 (NRF2) signaling pathway have antiviral effects, but the underlying antiviral mechanisms are incompletely understood. We evaluated the ability of the NRF2 activators 4-octyl itaconate (4OI), bardoxolone methyl (BARD), sulforaphane (SFN), and the inhibitor of exportin-1 (XPO1)-mediated nuclear export selinexor (SEL) to interfere with influenza virus A/Puerto Rico/8/1934 (H1N1) infection of human cells. All compounds reduced viral titers in supernatants from A549 cells and vascular endothelial cells in the order of efficacy SEL>4OI>BARD = SFN, which correlated with their ability to prevent nucleo-cytoplasmic export of viral nucleoprotein and the host cell protein p53. In contrast, intracellular levels of viral HA mRNA and nucleocapsid protein (NP) were unaffected. Knocking down mRNA encoding KEAP1 (the main inhibitor of NRF2) or inactivating the NFE2L2 gene (which encodes NRF2) revealed that physiologic NRF2 signaling restricts IAV replication. However, the antiviral effect of all compounds was NRF2-independent. Instead, XPO1 knock-down greatly reduced viral titers, and incubation of Calu3 cells with an alkynated 4OI probe demonstrated formation of a covalent complex with XPO1. Ligand-target modelling predicted covalent binding of all three NRF2 activators and SEL to the active site of XPO1 involving the critical Cys528. SEL and 4OI manifested the highest binding energies, whereby the 4-octyl tail of 4OI interacted extensively with the hydrophobic groove of XPO1, which binds nuclear export sequences on cargo proteins. Conversely, SEL as well as the three NRF2 activators were predicted to covalently bind the functionally critical Cys151 in KEAP1. Blocking XPO1-mediated nuclear export may, thus, constitute a "noncanonical" mechanism of anti-influenza activity of electrophilic NRF2 activators that can interact with similar cysteine environments at the active sites of XPO1 and KEAP1. Considering the importance of XPO1 function to a variety of pathogenic viruses, compounds that are optimized to inhibit both targets may constitute an important class of broadly active host-directed treatments that embody anti-inflammatory, cytoprotective, and antiviral properties.

Amino acid positions near the active site determine the reduced activity of human ACOD1 compared to murine ACOD1

cis-Aconitate decarboxylase (ACOD1, IRG1) converts cis-aconitate to the immunomodulatory and antibacterial metabolite itaconate. Although the active site residues of human and mouse ACOD1 are identical, the mouse enzyme is about fivefold more active. Aiming to identify the cause of this difference, we mutated positions near the active site in human ACOD1 to the corresponding residues of mouse ACOD1 and measured resulting activities in vitro and in transfected cells. Interestingly, Homo sapiens is the only species with methionine instead of isoleucine at residue 154 and introduction of isoleucine at this position increased the activity of human ACOD1 1.5-fold in transfected cells and 3.5-fold in vitro. Enzyme activity of gorilla ACOD1, which is almost identical to the human enzyme but has isoleucine at residue 154, was similar to the mouse enzyme in vitro. Met154 in human ACOD1 forms a sulfur-π bond to Phe381, which is positioned to impede access of the substrate to the active site. It appears that the ACOD1 sequence has changed at position 154 during human evolution, resulting in a pronounced decrease in activity. This change might have offered a selective advantage in diseases such as cancer.

Dimethyl fumarate and 4-octyl itaconate are anticoagulants that suppress Tissue Factor in macrophages via inhibition of Type I Interferon

Excessive inflammation-associated coagulation is a feature of infectious diseases, occurring in such conditions as bacterial sepsis and COVID-19. It can lead to disseminated intravascular coagulation, one of the leading causes of mortality worldwide. Recently, type I interferon (IFN) signaling has been shown to be required for tissue factor (TF; gene name F3) release from macrophages, a critical initiator of coagulation, providing an important mechanistic link between innate immunity and coagulation. The mechanism of release involves type I IFN-induced caspase-11 which promotes macrophage pyroptosis. Here we find that F3 is a type I IFN-stimulated gene. Furthermore, F3 induction by lipopolysaccharide (LPS) is inhibited by the anti-inflammatory agents dimethyl fumarate (DMF) and 4-octyl itaconate (4-OI). Mechanistically, inhibition of F3 by DMF and 4-OI involves suppression of Ifnb1 expression. Additionally, they block type I IFN- and caspase-11-mediated macrophage pyroptosis, and subsequent TF release. Thereby, DMF and 4-OI inhibit TF-dependent thrombin generation. In vivo, DMF and 4-OI suppress TF-dependent thrombin generation, pulmonary thromboinflammation, and lethality induced by LPS, E. coli, and S. aureus, with 4-OI additionally attenuating inflammation-associated coagulation in a model of SARS-CoV-2 infection. Our results identify the clinically approved drug DMF and the pre-clinical tool compound 4-OI as anticoagulants that inhibit TF-mediated coagulopathy via inhibition of the macrophage type I IFN-TF axis.

Itaconate family-based host-directed therapeutics for infections

Itaconate is a crucial anti-infective and anti-inflammatory immunometabolite that accumulates upon disruption of the Krebs cycle in effector macrophages undergoing inflammatory stress. Esterified derivatives of itaconate (4-octyl itaconate and dimethyl itaconate) and its isomers (mesaconate and citraconate) are promising candidate drugs for inflammation and infection. Several itaconate family members participate in host defense, immune and metabolic modulation, and amelioration of infection, although opposite effects have also been reported. However, the precise mechanisms by which itaconate and its family members exert its effects are not fully understood. In addition, contradictory results in different experimental settings and a lack of clinical data make it difficult to draw definitive conclusions about the therapeutic potential of itaconate. Here we review how the immune response gene 1-itaconate pathway is activated during infection and its role in host defense and pathogenesis in a context-dependent manner. Certain pathogens can use itaconate to establish infections. Finally, we briefly discuss the major mechanisms by which itaconate family members exert antimicrobial effects. To thoroughly comprehend how itaconate exerts its anti-inflammatory and antimicrobial effects, additional research on the actual mechanism of action is necessary. This review examines the current state of itaconate research in infection and identifies the key challenges and opportunities for future research in this field.

The immunometabolite itaconate stimulates OXGR1 to promote mucociliary clearance during the pulmonary innate immune response

Pathogens and inflammatory conditions rapidly induce the expression of immune-responsive gene 1 (IRG1) in cells of myeloid lineage. IRG1 encodes an aconitate decarboxylase (ACOD1) that produces the immunomodulatory metabolite itaconate (ITA). In addition to rapid intracellular accumulation, ITA is also secreted from the cell, but whether secreted ITA functions as a signaling molecule is unclear. Here, we identified ITA as an orthosteric agonist of the GPCR OXGR1, with an EC50 of approximately 0.3 mM, which was in the same range as the physiological concentration of extracellular ITA upon macrophage activation. ITA activated OXGR1 to induce Ca2+ mobilization, ERK phosphorylation, and endocytosis of the receptor. In a mouse model of pulmonary infection with bacterial Pseudomonas aeruginosa, ITA stimulated Oxgr1-dependent mucus secretion and transport in respiratory epithelium, the primary innate defense mechanism of the airway. Our study thus identifies ITA as a bona fide ligand for OXGR1 and the ITA/OXGR1 paracrine signaling pathway during the pulmonary innate immune response.

Dimethyl itaconate is effective in host-directed antimicrobial responses against mycobacterial infections through multifaceted innate immune pathways

BACKGROUND

Itaconate, a crucial immunometabolite, plays a critical role in linking immune and metabolic functions to influence host defense and inflammation. Due to its polar structure, the esterified cell-permeable derivatives of itaconate are being developed to provide therapeutic opportunities in infectious and inflammatory diseases. Yet, it remains largely uncharacterized whether itaconate derivatives have potentials in promoting host-directed therapeutics (HDT) against mycobacterial infections. Here, we report dimethyl itaconate (DMI) as the promising candidate for HDT against both Mycobacterium tuberculosis (Mtb) and nontuberculous mycobacteria by orchestrating multiple innate immune programs.

RESULTS

DMI per se has low bactericidal activity against Mtb, M. bovis Bacillus Calmette-Guérin (BCG), and M. avium (Mav). However, DMI robustly activated intracellular elimination of multiple mycobacterial strains (Mtb, BCG, Mav, and even to multidrug-resistant Mtb) in macrophages and in vivo. DMI significantly suppressed the production of interleukin-6 and -10, whereas it enhanced autophagy and phagosomal maturation, during Mtb infection. DMI-mediated autophagy partly contributed to antimicrobial host defenses in macrophages. Moreover, DMI significantly downregulated the activation of signal transducer and activator of transcription 3 signaling during infection with Mtb, BCG, and Mav.

CONCLUSION

Together, DMI has potent anti-mycobacterial activities in macrophages and in vivo through promoting multifaceted ways for innate host defenses. DMI may bring light to new candidate for HDT against Mtb and nontuberculous mycobacteria, both of which infections are often intractable with antibiotic resistance.

Itaconate Suppresses the Activation of Mitochondrial NLRP3 Inflammasome and Oxidative Stress in Allergic Airway Inflammation

Itaconate has emerged as a novel anti-inflammatory and antioxidative endogenous metabolite, yet its role in allergic airway inflammation (AAI) and the underlying mechanism remains elusive. Here, the itaconate level in the lung was assessed by High Performance Liquid Chromatography (HPLC), and the effects of the Irg1/itaconate pathway on AAI and alveolar macrophage (AM) immune responses were evaluated using an ovalbumin (OVA)-induced AAI model established by wild type (WT) and Irg1-/- mice, while the mechanism of this process was investigated by metabolomics analysis, mitochondrial/cytosolic protein fractionation and transmission electron microscopy in the lung tissues. The results demonstrated that the Irg1 mRNA/protein expression and itaconate production in the lung were significantly induced by OVA. Itaconate ameliorated while Irg1 deficiency augmented AAI, and this may be attributed to the fact that itaconate suppressed mitochondrial events such as NLRP3 inflammasome activation, oxidative stress and metabolic dysfunction. Furthermore, we identified that the Irg1/itaconate pathway impacted the NLRP3 inflammasome activation and oxidative stress in AMs. Collectively, our findings provide evidence for the first time, supporting the conclusion that in the allergic lung, the itaconate level is markedly increased, which directly regulates AMs' immune responses. We therefore propose that the Irg1/itaconate pathway in AMs is a potential anti-inflammatory and anti-oxidative therapeutic target for AAI.

Immunometabolic Signature during Respiratory Viral Infection: A Potential Target for Host-Directed Therapies

RNA viruses are known to induce a wide variety of respiratory tract illnesses, from simple colds to the latest coronavirus pandemic, causing effects on public health and the economy worldwide. Influenza virus (IV), parainfluenza virus (PIV), metapneumovirus (MPV), respiratory syncytial virus (RSV), rhinovirus (RhV), and coronavirus (CoV) are some of the most notable RNA viruses. Despite efforts, due to the high mutation rate, there are still no effective and scalable treatments that accompany the rapid emergence of new diseases associated with respiratory RNA viruses. Host-directed therapies have been applied to combat RNA virus infections by interfering with host cell factors that enhance the ability of immune cells to respond against those pathogens. The reprogramming of immune cell metabolism has recently emerged as a central mechanism in orchestrated immunity against respiratory viruses. Therefore, understanding the metabolic signature of immune cells during virus infection may be a promising tool for developing host-directed therapies. In this review, we revisit recent findings on the immunometabolic modulation in response to infection and discuss how these metabolic pathways may be used as targets for new therapies to combat illnesses caused by respiratory RNA viruses.

Protein targeting by the itaconate family in immunity and inflammation

Immune cells are metabolically plastic and respond to inflammatory stimuli with large shifts in metabolism. Itaconate is one of the most up-regulated metabolites in macrophages in response to the gram negative bacterial product LPS. As such, itaconate has recently been the subject of intense research interest. The artificial derivatives, including 4-Octyl Itaconate (4-OI) and Dimethyl Itaconate (DI) and naturally produced isomers, mesaconate and citraconate, have been tested in relation to itaconate biology with similarities and differences in the biochemistry and immunomodulatory properties of this family of compounds emerging. Both itaconate and 4-OI have been shown to modify cysteines on a range of target proteins, with the modification being linked to a functional change. Targets include KEAP1 (the NRF2 inhibitor), GAPDH, NLRP3, JAK1, and the lysosomal regulator, TFEB. 4-OI and DI are more electrophilic, and are therefore stronger NRF2 activators, and inhibit the production of Type I IFNs, while itaconate inhibits SDH and the dioxygenase, TET2. Additionally, both itaconate and derivates have been shown to be protective across a wide range of mouse models of inflammatory and infectious diseases, through both distinct and overlapping mechanisms. As such, continued research involving the comparison of itaconate and related molecules holds exciting prospects for the study of cysteine modification and pathways for immunomodulation and the potential for new anti-inflammatory therapeutics.

Itaconate derivative 4-OI inhibits PRRSV proliferation and associated inflammatory response

Itaconate, a metabolite of the tricarboxylic acid (TCA) cycle produced by immunoresponsive gene 1 (IRG1) via catalyzation of cis-aconitate, plays important roles in metabolism and immunity. Porcine reproductive and respiratory syndrome virus (PRRSV) is an Arterivirus that has devastated the swine industry worldwide for over 30 years. Here, we found that 4-octyl itaconate (4-OI), a cell-permeable itaconate derivative, dose-dependently inhibited PRRSV proliferation by interfering with viral attachment, replication, and release. Furthermore, 4-OI suppressed the PRRSV-induced inflammatory response by enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) signaling. Interestingly, PRRSV infection caused a reduction in itaconate abundance and simultaneously led to an accumulation of cis-aconitate, the upstream metabolite of itaconate, and both of these effects were accomplished by downregulating IRG1 expression. Taken together, these results demonstrate that 4-OI not only inhibits PRRSV replication but also suppresses PRRSV-induced inflammatory responses, indicating that 4-OI is a promising drug candidate for combating PRRSV.

The role of immunomodulatory metabolites in shaping the inflammatory response of macrophages

Macrophage activation has long been implicated in a myriad of human pathophysiology, particularly in the context of the dysregulated capacities of an unleashing intracellular or/and extracellular inflammatory response. A growing number of studies have functionally coupled the macrophages' inflammatory capacities with dynamic metabolic reprogramming which occurs during activation, albeit the results have been mostly interpreted through classic metabolism point of view; macrophages take advantage of the rewired metabolism as a source of energy and for biosynthetic precursors. However, a specific subset of metabolic products, namely immune-modulatory metabolites, has recently emerged as significant regulatory signals which control inflammatory responses in macrophages and the relevant extracellular milieu. In this review, we introduce recently highlighted immuno-modulatory metabolites, with the aim of understanding their physiological and pathological relevance in the macrophage inflammatory response. [BMB Reports 2022; 55(11): 519-527].

Correction: Itaconate and derivatives reduce interferon responses and inflammation in influenza A virus infection

[This corrects the article DOI: 10.1371/journal.ppat.1010219.].

The signaling pathways and therapeutic potential of itaconate to alleviate inflammation and oxidative stress in inflammatory diseases

Endogenous small molecules are metabolic regulators of cell function. Itaconate is a key molecule that accumulates in cells when the Krebs cycle is disrupted. Itaconate is derived from cis-aconitate decarboxylation by cis-aconitate decarboxylase (ACOD1) in the mitochondrial matrix and is also known as immune-responsive gene 1 (IRG1). Studies have demonstrated that itaconate plays an important role in regulating signal transduction and posttranslational modification through its immunoregulatory activities. Itaconate is also an important bridge among metabolism, inflammation, oxidative stress, and the immune response. This review summarizes the structural characteristics and classical pathways of itaconate, its derivatives, and the compounds that release itaconate. Here, the mechanisms of itaconate action, including its transcriptional regulation of ATF3/IκBζ axis and type I IFN, its protein modification regulation of KEAP1, inflammasome, JAK1/STAT6 pathway, TET2, and TFEB, and succinate dehydrogenase and glycolytic enzyme metabolic action, are presented. Moreover, the roles of itaconate in diseases related to inflammation and oxidative stress induced by autoimmune responses, viruses, sepsis and IRI are discussed in this review. We hope that the information provided in this review will help increase the understanding of cellular immune metabolism and improve the clinical treatment of diseases related to inflammation and oxidative stress.

The role of immunomodulatory metabolites in shaping the inflammatory response of macrophages

Macrophage activation has long been implicated in a myriad of human pathophysiology, particularly in the context of the dysregulated capacities of an unleashing intracellular or/and extracellular inflammatory response. A growing number of studies have functionally coupled the macrophages' inflammatory capacities with dynamic metabolic reprogramming which occurs during activation, albeit the results have been mostly interpreted through classic metabolism point of view; macrophages take advantage of the rewired metabolism as a source of energy and for biosynthetic precursors. However, a specific subset of metabolic products, namely immune-modulatory metabolites, has recently emerged as significant regulatory signals which control inflammatory responses in macrophages and the relevant extracellular milieu. In this review, we introduce recently highlighted immuno-modulatory metabolites, with the aim of understanding their physiological and pathological relevance in the macrophage inflammatory response. [BMB Reports 2022; 55(11): 519-527].

Innate metabolic responses against viral infections

Metabolic adaptation to viral infections critically determines the course and manifestations of disease. At the systemic level, a significant feature of viral infection and inflammation that ensues is the metabolic shift from anabolic towards catabolic metabolism. Systemic metabolic sequelae such as insulin resistance and dyslipidaemia represent long-term health consequences of many infections such as human immunodeficiency virus, hepatitis C virus and severe acute respiratory syndrome coronavirus 2. The long-held presumption that peripheral and tissue-specific 'immune responses' are the chief line of defence and thus regulate viral control is incomplete. This Review focuses on the emerging paradigm shift proposing that metabolic engagements and metabolic reconfiguration of immune and non-immune cells following virus recognition modulate the natural course of viral infections. Early metabolic footprints are likely to influence longer-term disease manifestations of infection. A greater appreciation and understanding of how local biochemical adjustments in the periphery and tissues influence immunity will ultimately lead to interventions that curtail disease progression and identify new and improved prognostic biomarkers.

Regulation of innate immunity by Nrf2

The transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) has been mainly investigated as a regulator of redox homeostasis. However, research over the past years has implicated Nrf2 as an important regulator of innate immunity. Here, we discuss the role of Nrf2 in the innate immune response, highlighting the interaction between Nrf2 and major components of the innate immune system. Indeed, Nrf2 has been shown to widely control the immune response by interacting directly or indirectly with important innate immune components, including the toll-like receptors-Nuclear factor kappa B (NF-kB) pathway, inflammasome signaling, and the type-I interferon response. This indicates an essential role for Nrf2 in diseases related to microbial infections, inflammation, and cancer. Yet, further studies are required to determine the exact mechanism underpinning the interactions between Nrf2 and innate immune players in order to allow a better understanding of these diseases and leverage new therapeutic strategies.

Macrophage Polarization and Reprogramming in Acute Inflammation: A Redox Perspective

Macrophage polarization refers to the process by which macrophages can produce two distinct functional phenotypes: M1 or M2. The balance between both strongly affects the progression of inflammatory disorders. Here, we review how redox signals regulate macrophage polarization and reprogramming during acute inflammation. In M1, macrophages augment NADPH oxidase isoform 2 (NOX2), inducible nitric oxide synthase (iNOS), synaptotagmin-binding cytoplasmic RNA interacting protein (SYNCRIP), and tumor necrosis factor receptor-associated factor 6 increase oxygen and nitrogen reactive species, which triggers inflammatory response, phagocytosis, and cytotoxicity. In M2, macrophages down-regulate NOX2, iNOS, SYNCRIP, and/or up-regulate arginase and superoxide dismutase type 1, counteract oxidative and nitrosative stress, and favor anti-inflammatory and tissue repair responses. M1 and M2 macrophages exhibit different metabolic profiles, which are tightly regulated by redox mechanisms. Oxidative and nitrosative stress sustain the M1 phenotype by activating glycolysis and lipid biosynthesis, but by inhibiting tricarboxylic acid cycle and oxidative phosphorylation. This metabolic profile is reversed in M2 macrophages because of changes in the redox state. Therefore, new therapies based on redox mechanisms have emerged to treat acute inflammation with positive results, which highlights the relevance of redox signaling as a master regulator of macrophage reprogramming.

Itaconate Isomers in Bread

The naturally occurring isomers itaconate, mesaconate and citraconate possess immunomodulatory, antioxidative and antimicrobial properties. However, it is not known whether they occur in commonly consumed human foods. Considering that they can arise as a result of heat conversion, we tested whether they occur in bread, representing a commonly consumed baked good. Using high-performance liquid chromatography−tandem mass spectrometry, we measured concentrations of the three isomers and their potential precursors, citrate and cis-aconitate, in unbaked sourdough and dough, and in crumb and crust of baked bread. All three isomers were detected at low concentrations (<20 pmol/mg dry weight) in sourdough, dough, crumb and crust. Concentrations of itaconate and citraconate were substantially higher in crust than in crumb of wheat and rye bread, and a modest increase in mesaconate was observed in crust of rye bread. In contrast, cis-aconitate concentrations were considerably lower in crust, which was consistent with the conversion of cis-aconitate to itaconate isomers due to higher temperature of the dough surface during baking. Based on data on the average consumption of bread and related baked goods in Germany, the daily intake of itaconate isomers was estimated to be roughly 7−20 µg. Thus, baked goods constitute a regular dietary source of low amounts of itaconate isomers. In order to enable studies on the impact of dietary intake of itaconate isomers on human health, their concentrations should be assessed in other foods that are subjected to high heating.

ISG15 deficiency features a complex cellular phenotype that responds to treatment with itaconate and derivatives

Background

Congenital ISG15 deficiency is a rare autoinflammatory disorder that is driven by chronically elevated systemic interferon levels and predominantly affects central nervous system and skin.

Methods and results

We have developed induced pluripotent stem cell‐derived macrophages and endothelial cells as a model to study the cellular phenotype of ISG15 deficiency and identify novel treatments. ISG15^–/– macrophages exhibited the expected hyperinflammatory responses, but normal phagocytic function. In addition, they displayed a multifaceted pathological phenotype featuring increased apoptosis/pyroptosis, oxidative stress, glycolysis, and acylcarnitine levels, but decreased glutamine uptake, BCAT1 expression, branched chain amino acid catabolism, oxidative phosphorylation, β‐oxidation, and NAD(P)H‐dependent oxidoreductase activity. Furthermore, expression of genes involved in mitochondrial biogenesis and respiratory chain complexes II–V was diminished in ISG15^–/– cells. Defective mitochondrial respiration was restored by transduction with wild‐type ISG15, but only partially by a conjugation‐deficient variant, suggesting that some ISG15 functions in mitochondrial respiration require ISGylation to cellular targets. Treatment with itaconate, dimethyl‐itaconate, 4‐octyl‐itaconate, and the JAK1/2 inhibitor ruxolitinib ameliorated increased inflammation, propensity for cell death, and oxidative stress. Furthermore, the treatments greatly improved mitochondria‐related gene expression, BCAT1 levels, redox balance, and intracellular and extracellular ATP levels. However, efficacy differed among the compounds according to read‐out and cell type, suggesting that their effects on cellular targets are not identical. Indeed, only itaconates increased expression of anti‐oxidant genes NFE2L2, HMOX1, and GPX7, and dimethyl‐itaconate improved redox balance the most. Even though itaconate treatments normalized the elevated expression of interferon‐stimulated genes, ISG15^–/– macrophages maintained their reduced susceptibility to influenza virus infection.

Conclusions

These findings expand the cellular phenotype of human ISG15 deficiency and reveal the importance of ISG15 for regulating oxidative stress, branched chain amino acid metabolism, and mitochondrial function in humans. The results validate ruxolitinib as treatment for ISG15 deficiency and suggest itaconate‐based medications as additional therapeutics for this rare disorder.